Generally, an organic electroluminescence display, which is one of flat plate displays, is configured in a way that an organic electroluminescence layer is inserted between a cathode layer and an anode layer on a transparent substrate. The organic electroluminescence display has a very thin thickness and, further, can be formed in a matrix type. Further, the organic electroluminescence display can be driven by a low voltage below 15 V, and has more excellent characteristics in a brightness, a viewing angle, a response time, a power consumption, or the like in comparison with TFT-LCD. Especially, the organic electroluminescence display has a fast response time of 1 μs in comparison with other displays and, accordingly, is very suitable for a next generation multimedia display to which a function of moving pictures is essential.
Since, however, an organic light-emitting layer and a cathode layer of the organic electroluminescence display are vulnerable to oxygen and moisture, an exposure to outer air should be excluded during a fabricating process in order to secure a reliability of the organic electroluminescence display. Hence, the fabricating process of the organic electroluminescence display is unable in general to use a photolithography for a pixellation or a patterning process.
The pixellation of the organic layer and the cathode layer of the organic electroluminescence display uses a direct pixellation using a shadow mask instead of the photolithography including a masking process and an etching process in which the organic layer and the cathode layer are exposed to oxygen and moisture. However, such a method is inadaptable to use if a pitch between pixels, i.e., an interval between lines constituting the organic layer and the cathode layer, is reduced to realize a high resolution.
One of the general methods of patterning the organic electroluminescence display is carried out in a manner that an insulating layer of an electrically insulating material and a separator are formed on an anode layer and a substrate and, then, a cathode layer is patterned by using the separator.
In this method, the insulating layer is formed on an entire area of the anode layer except a dot-shaped opening. In this case, the insulating layer defines pixels by the opening and inhibits a leakage current from edges of the cathodes. Further, the insulating layer prevents the cathode layer from being short-circuited with the anode layer at a boundary since the stacked organic layer becomes thinner near the separator due to a shadow effect by the separator in a direction perpendicular to the anode layer formed for patterning of the cathode layer.
Furthermore, the insulating layer should not have an overhang structure in order to prevent a cathode layer that will be formed later from being cut. Therefore, the insulating layer is generally formed of a positive photoresist material so as to have a positive profile.
The separator formed on the insulating layer crosses with the anode layer to be arranged so as to separate by a predetermined distance from each other as well as has the overhang structure so as not to make the cathode layer be short-circuited with an adjacent component. Especially, unlike a general patterning process, a negative profile should be constantly maintained in the separator in order to prevent the short circuit between adjacent cathode layer lines. If the separator is lost, there occurs a short-circuit between adjacent pixels. A negative photoresist material is used for the separator having the overhang structure.
In order to fabricate the organic electroluminescence display stably, both of the insulating layer and the separator are necessary. Yet, the photolithographic process is required for each process for fabricating the insulating layer and the separator, so that a fabricating process of the organic electroluminescence display becomes complicated and a product cost thereof increases.
Hereinafter, a fabricating method of a first conventional organic electroluminescence display will be described with reference to the accompanying drawings.
FIG. 1 is a plan view of the first conventional organic electroluminescence display.
As illustrated in FIG. 1, a plurality of first electrodes 12 that have a specific width and are formed of indium tin oxide (ITO) or the like are arranged on a transparent substrate 11 in a stripe type. An insulating pattern 13 of lattice type is stacked on the transparent substrate 11 having the first electrodes 12 in an area between the adjacent first electrodes 12 and an area crossing with the first electrodes 12. Moreover, separators 14 are formed in an area of the insulating pattern 13 crossing with the first electrodes 12.
Furthermore, organic light-emitting layers and second electrodes (not shown) are formed on the first electrodes 12 including the insulating pattern 13 and the separators 14.
Referring to FIGS. 2A to 2C and 3A to 3C, the fabricating method of the first conventional organic electroluminescence display will be described in detail as follows.
FIGS. 2A to 2C provide cross-sectional views illustrating a process of the fabricating method of the first conventional organic electroluminescence display, which are taken along the line A-A in FIG. 1.
FIGS. 3A to 3C depict cross-sectional views illustrating the process of the fabricating method of the first conventional organic electroluminescence display, which are taken along the line B-B in FIG. 1.
As shown in FIGS. 2A and 3A, an anode layer (not shown) made of indium tin oxide (ITO) or the like is stacked with a predetermined thickness on the transparent substrate 11 by a sputtering. A photoresist (not shown) is coated on the entirely deposited anode layer. The photoresist is exposed with a mask and developed, thereby forming a stripe type photoresist pattern (not shown). The anode layer is etched by using the photoresist pattern as a mask and a remaining photoresist is removed, thereby forming the stripe type first electrodes 12.
As illustrated in FIGS. 2B and 3B, an electrically insulating layer (not shown) is stacked on the transparent substrate 11 including the first electrodes 12. The insulating layer can be formed of an organic or an inorganic material. As for the organic material, an acrylic-, a novolak-, an epoxy- and a polyimide-based photoresist or the like is used. As the inorganic material, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or the like is used. Next, by patterning the insulating layer, the lattice type insulating pattern 13 except the dot-shaped openings formed on the first electrodes 12 is formed on the first electrodes 12 and the transparent substrate 11 in an area between the adjacent first electrodes 12 and an area crossing with the first electrodes 12 at regular intervals.
As depicted in FIGS. 2C and 3C, an organic photoresist of negative type (not shown) as an electrically insulating material is stacked on the insulating pattern 13, and then a patterning process is carried out, thereby forming the separators 14 having a negative profile. In this case, the separators 14 cross with the first electrodes 12 and are arranged at regular intervals on the insulating pattern 13 between the dot-shaped openings. Further, the separators 14 have the overhang structure so as to prevent second electrodes 16 from being short-circuited with adjacent components. Thereafter, organic light-emitting layers 15 and the second electrodes 16 are stacked in order on an entire surface including the first electrodes 12 by using a shadow mask (not shown). In this connection, if the organic light-emitting layers 15 are stacked on the first electrode 12, a thickness of the organic light-emitting layers 15 become thinner near the separators due to the shadow effect by the separators, so that the second electrodes 16 stacked on the organic light-emitting layers 15 can be short-circuited at a boundary with the first electrodes 12. The insulating pattern 13 serves to prevent such short circuit.
Next, an encapsulation plate formed of a metal, a glass, or the like or a passivation layer formed of an organic or an inorganic thin film is formed on an entire surface including the second electrodes 16 in order to airtightly protect the organic light-emitting layers 15 and the second electrodes 16 vulnerable to moisture and oxygen from an outside.
In the aforementioned first conventional organic electroluminescence display and the fabricating method thereof, the photolithographic process needs to be carried out twice in order to form the insulating pattern and the separators, which results in a complex fabricating process and a high cost of materials. In addition, since the two layers of the insulating pattern and the separators are formed by respective patterning processes, an adhesion therebetween becomes poor.
FIG. 4 depicts a plan view of a second conventional organic electroluminescence display. FIGS. 5A, 5B and 5C present cross-sectional views illustrating the second conventional organic electroluminescence display, which are taken along the lines A-A′, B-B′ and C-C′ in FIG. 4, respectively.
As shown in FIGS. 4 and 5A to 5C, a plurality of first electrodes 42 that have a specific width and are formed of indium tin oxide (ITO) or the like are arranged on a transparent substrate 41 in a stripe type. A lattice type insulating pattern 43 is stacked on the transparent substrate 41 having the first electrodes 42 in an area between the adjacent first electrodes 42 and an area crossing with the first electrodes 42. Moreover, formed on the first electrodes 42 are openings 45 for exposing an area where pixels are formed. Therefore, the insulating pattern 43 in which the openings 45 where pixels are formed is exposed has a lattice shape.
Further, an insulating pattern 43a stacked in a direction in parallel with the plurality of first electrodes 42 is formed by using a half tone exposure mask having a rectangular-, a slit- and a chevron-shaped half tone pattern. An insulating pattern 43b formed in a direction crossing with the first electrodes 42 is formed in a normal tone pattern. At this time, the insulating pattern 43a has a thickness thinner than that of the insulating pattern 43b. This is for excluding a possibility of an open circuit occurring since a thickness of the second electrodes formed in a direction crossing with the first electrodes 42 becomes thinner when the second electrodes (not shown) are deposited at a boundary between edges of the photoresist and the first electrodes 42.
Hereinafter, a fabricating method of the second conventional organic electroluminescence display illustrated in FIG. 4 will be described in detail with reference to FIGS. 6A to 6D and 7A to 7D.
FIGS. 6A to 6D represent cross-sectional views showing a process of the fabricating method of the second conventional organic electroluminescence display, which is taken along the line A-A′ in FIG. 4. FIGS. 7A to 7D offer cross-sectional views illustrating the process of the fabricating method of the second conventional organic electroluminescence display, which is taken along the line B-B′ in FIG. 4.
As shown in FIGS. 6A and 7A, the transparent substrate 41 that has been cleaned is prepared. In the present invention, a transparent glass substrate is used for the transparent substrate 41. An anode layer (not shown) composed of indium tin oxide (ITO) or the like is entirely deposited on the transparent substrate 41 with a uniform thickness, and a photoresist (not illustrated in the drawing) is coated thereon. Then, an exposure and a development are carried out, thereby forming a photoresist pattern. The anode layer is etched by using such photoresist pattern as a mask and the photo-resist layer is removed, thereby forming the stripe type first electrodes 42.
As depicted in FIGS. 6B and 7B, an insulating layer forming process is carried out to inhibit a leakage current from the edges of the first electrodes 42 and to use, as a device separating layer, a photoresist (not shown) for an insulation between the first electrodes and the second electrode 48 that will be formed later.
In order to do so, a photoresist is coated on the transparent substrate 41, and the insulating pattern 43 is formed by using an exposure mask (not illustrated in the drawing). At this time, the insulating pattern 43a stacked in a direction in parallel with the first electrode 42 is formed by using the half tone exposure mask of a rectangular-, a slit- and a chevron-shaped half tone pattern. Further, the insulating pattern 43a formed in the half tone pattern is formed with a thickness thinner than that of the insulating pattern 43b stacked in the direction crossing with the second electrodes. The thickness of the insulating pattern 43a formed in the half tone pattern is determined by controlling an opening ratio of the half tone area described in the exposure mask.
The reason for reducing the thickness of the insulating pattern 43a is to exclude a possibility of the open circuit occurring since a film thickness of the plurality of the second electrodes 48 running on the openings 45 where organic light-emitting layers 47 are formed and crossing with the first electrodes 42 becomes thinner at a boundary between edges of the insulating pattern 43a and the first electrodes 42 when the second electrodes 48 are evaporated.
Thereafter, as shown in FIGS. 6C and 7C, the transparent substrate 41 is transferred inside a vacuum deposition apparatus. Then, the organic light-emitting layers 47 are formed on the first electrodes 42 through the openings of a first shadow mask 49 by using the insulating pattern 43b as a support of the first shadow mask 49. If the insulating pattern 43b is used as the support, it is possible to adhere closely to the first shadow mask 49 without causing any damage on the first electrodes 42, thereby enabling to prevent a lateral diffusion of the organic light-emitting layers 47.
In this case, the organic light-emitting layers 47 are formed of a fluorescent and a phosphorescent organic luminescent material with low molecular weight such as Alq3, Anthracene, Ir(ppy)3, or the like.
Next, as illustrated in FIGS. 6D and 7D, the second electrodes 48 are formed on the organic light-emitting layers 47 by using the insulating pattern 43b as a support of a second shadow mask 50 having a stripe type electrode pattern. If the insulating pattern 43b is used as the support, it is possible to adhere closely to the second shadow mask 50 without causing any damage on the organic light-emitting layers 47, thereby enabling to prevent a lateral diffusion of the second electrodes 48.
The second electrodes 48 mainly use a metal having an excellent electric conductivity such as Al, Li/Al, MgAg, Ca, or the like, and are stacked by a sputtering, an e-beam deposition, a thermal evaporation, or the like. And, an encapsulation layer made of a metal, a glass, or the like or a passivation layer formed of an organic or an inorganic material is formed on an entire surface including the second electrodes 48 so as to airtightly protect the organic light-emitting layers 47 vulnerable to moisture and oxygen from the outside.
In the aforementioned second conventional organic electroluminescence display and the fabricating method thereof, a single photolithographic process is carried out to form the insulating layer and the separators by using the half tone mask, so that the fabricating process becomes simple. Since the insulating layer and the separator are formed as a single layer, there is no problem of an adhesive strength therebetween. Further, since an alignment margin required for forming two separate layers of the insulating pattern and the separator is not needed, it is possible to increase an opening ratio of the organic electroluminescence display and a yield thereof.
However, there exist drawbacks in that it is difficult to design the half tone mask and, further, a product cost thereof increases in comparison with a conventional mask by about 1.5 times or more. Further, since there no overhang structure of the separators, a shadow mask is required for a patterning of the second electrodes. However, no shadow mask adaptable to a mass production of the organic electroluminescence display has been suggested.
FIG. 8 is a plan view of a third conventional organic electroluminescence display.
The third conventional organic electroluminescence display is formed by a method for forming a device separating layer of an electrically insulating property composed of an area having a thin thickness and a positive profile and an area having a negative profile and serving as a separator by employing an image reversal process using a half tone mask and an image reversal photoresist.
In general, in case of a positive photoresist, an exposed area is removed by a developer, and an area shielded by a mask pattern is formed as a pattern, wherein the pattern has a property of a positive profile. Meanwhile, in case of a negative photoresist, an exposed area is formed as a pattern that is insoluble in the developer by a cross-linking, wherein the pattern has a property of a negative profile.
However, in order that a single layer of insulating pattern serves as a general insulating layer and a separator as well, it should be made to have a positive profile in an area acting as the insulating layer and a negative profile in an area acting as the separator. To do so, a pattern having the positive profile needs to be formed in the single layer of the insulating pattern in advance. Then, by carrying out an image reversal, a flood exposure and a development thereto, the layer of the insulating pattern should be patterned to form the negative profile. Herein, the image reversal is carried out by an image reversal process using an image reversal photoresist or a general positive photosensitive material. Next, the image-reversed insulating pattern undergoes the flood exposure and the development so as to be patterned to form the negative profile.
In case of the typical image reversal using the image reversal photoresist, an initially formed photoresist has characteristics that a non-exposed portion does not dissolve and an exposed portion is developed, as in case of using the general positive photosensitive material. However, once the exposed portion of the photoresist is heated at a temperature over 115° C., the exposed portion becomes insoluble and, thus, the exposed portion is not developed by the developer. Herein, the change in the property of the exposed photoresist, i.e., from being soluble to being insoluble, by a heating is referred to as an image reversal and, further, the heating process for the image reversal is referred to as an image reversal baking. In the meantime, since the shield area still has a property of the positive photosensitive material, it does not dissolve in the developer. If the flood exposure is carried out on the photoresist, a portion having the changed property of being insoluble in the developer by the image reversal baking after the exposure has the same property even after the flood exposure. On the other hand, a portion shielded during the exposure has the property of the positive photosensitive material and, thus, is developed after the flood exposure. Accordingly, if the image reversal photoresist is used, the property of the positive photosensitive material is maintained at the beginning. However, after carrying out the exposure, the image reversal baking and the flood exposure, the exposed portion remains and the negative profile can be obtained, as same as the negative photosensitive material.
The image reversal method other than the method using the image reversal photoresist includes a method using an organic solvent instead of an aqueous developer and a method involving: coating and exposing a general positive photoresist; diffusing an image reversal base catalyst into the photoresist; carrying out an image reversal on the photoresist by performing the image reversal baking; and developing an unexposed area by carrying out the flood exposure.
A third conventional organic electroluminescence display employing the image reversal process using the image reversal photoresist will be described with reference to FIGS. 9A to 9C.
FIGS. 9A, 9B and 9C provide cross-sectional views of the third conventional organic electroluminescence display, which are taken along the lines A-A′, B-B′ and C-C′ in FIG. 8, respectively.
A plurality of first electrodes 62 that have a specific width and are formed of indium tin oxide (ITO) or the like are arranged on a transparent substrate 61 in a stripe type. A lattice type insulating pattern 63 is stacked on the transparent substrate 61 including the first electrodes 62 in an area between the adjacent first electrodes 62 and an area crossing with the first electrodes 62. Moreover, formed on the first electrodes 62 are openings 65 for exposing an area where pixels are formed. Therefore, the insulating pattern 63 in which the openings 45 where the pixels are formed is exposed has a lattice shape.
An insulating pattern 63a stacked in parallel with the first electrodes 62 is formed by using a half tone exposure mask having a rectangular-, a slit- or a chevron-shaped half tone pattern. Further, an insulating pattern 63b stacked in a direction crossing with the first electrodes 62 is formed in a normal tone pattern. The insulating pattern 63a formed in the half tone pattern is formed with a thickness thinner than that of the insulating pattern 63b stacked in a direction crossing with the first electrodes. The thickness of the insulating pattern 63a is determined by controlling an opening ratio of the half tone area described in the exposure mask.
Trenches 66 are formed at a central portion of the insulating pattern 63b stacked in a direction crossing with the first electrodes 62. Herein, an area having the trenches thereon is formed in a manner that the insulating pattern 63b undergoes an exposure using a stripe type mask, an image reversal by a heating, a flood exposure and a development. A certain portion of the photoresist remains inside such area thus formed, thereby forming the trenches 66 of the negative profile having the overhang structure.
The trenches 66 have a function of preventing a short circuit between the second electrodes adjacent to each other. Herein, organic light-emitting layers and the second electrodes (cathode layers) (not shown) are formed on the transparent substrate 61 including the openings 65.
Referring to FIGS. 10A to 10C and 11A to 11C, the third conventional organic electroluminescence display illustrated in FIG. 8 will be described in detail.
FIGS. 10A to 10C present cross-sectional views illustrating a process of a fabricating method of the third conventional organic electroluminescence display, which are taken along the line A-A′ in FIG. 8.
FIGS. 11A to 11C represent cross-sectional views illustrating the process of the fabricating method of the third conventional organic electroluminescence display, which are taken along the line B-B′ in FIG. 8.
As can be seen from FIGS. 10A and 11A, an anode layer formed of indium tin oxide (ITO) or the like is stacked on the transparent substrate 61, and a photoresist (not shown) is coated thereon. Then, an exposure and a development to the photoresist are carried out, thereby forming a stripe type photoresist pattern. Thereafter, the anode layer is etched by using such photoresist pattern as a mask and the photoresist pattern is removed, to thereby form the stripe type first electrodes 62.
As can be seen from FIGS. 10B and 11B, an insulating layer forming process is carried out inhibit a leakage current from edges of the first electrodes 62 and use, as a device separation structure layer, a photoresist (not shown) having an electrically insulating characteristic to prevent an electrical connection between the first electrodes 62 and the second electrodes 68 that will be formed later.
The image-reversed photoresist is coated on the transparent substrate 61 having the first electrodes 62 formed thereon. After coating the photoresist on the transparent substrate 61, a prebaking is carried out at 100° C. for about 60 seconds so as to dry the photoresist. And, the insulating pattern 63 is formed by using a first exposure mask. The insulating pattern 63a stacked in parallel with the first electrodes 62 is formed in a half tone pattern by using an exposure mask having a rectangular-, a slit- or a chevron-shaped half tone pattern. The insulating pattern 63a is formed with a thickness thinner than that of the insulating pattern 63b crossing with the first electrodes 62. The thickness of the half tone insulating pattern 63a is determined by controlling an opening ratio of a half tone area described in the exposure mask.
The reason for lowering the insulating pattern 63a in a direction in parallel with the first electrodes 61 than the insulating pattern 63b in a direction crossing with the first electrodes 62 is to exclude a possibility of the open circuit occurring since a thickness of the second electrode 68 becomes thinner when the second electrode 68 is deposited at a boundary between edges of the insulating pattern 63a and the first electrodes 62.
As depicted in FIGS. 10C and 11C, after the completion of the development, a dry process such as an air knife or a spin dry is carried out on the transparent substrate 61 at a temperature lower than 100° C. And, a second exposure process is carried out by using a second exposure mask for use in a device separating layer. After the completion of the second exposure process, a reversal baking is carried out for about 120 seconds at 120° C. A flood exposure is then carried out so as to change the property of the photoresist. Since the reversal baking for an image reversal and then the flood exposure are carried out, the property of the photoresist is changed in a manner that an exposed portion remains but a non-exposed portion is developed. In the second exposure process, the trenches are formed at a central portion of the normal tone insulating pattern 63b stacked in a direction perpendicular to the first electrodes 62 by carrying out an exposure with a width narrower than that of the insulating pattern 63b. 
The trenches 66 for an isolation of adjacent pixels are formed at the central portion of the normal tone insulating pattern 63b stacked in a direction perpendicular to the first electrodes 62 by a development process, wherein the trenches have a negative profile of an overhang structure. When the trenches 66 for the isolation of the adjacent pixels are formed, a depth of the trenches 66 is preferably greater than a sum of a deposition thickness of the organic light-emitting layers 67 and the second electrodes 68 that will be deposited later in order to exclude a possibility of a short circuit with the adjacent pixels. Specifically, the depth of the trenches 66 is preferably greater than the sum of the thickness of the organic light-emitting layers 67 and the second electrodes 68 by 1.5 to 5 times.
Subsequently, the transparent substrate 61 is subject to a post baking process and is transferred to a vacuum deposition apparatus. The organic light-emitting layers 67 are formed on the transparent substrate 61.
Next, the second electrodes 68 are formed on the transparent substrate 61 including the organic light-emitting layers 67. The second electrodes 68 mainly use a metal having an excellent electric conductivity such as Al, Li/Al, MgAg, Ca, or the like, and are stacked by a sputtering, an e-beam deposition, a thermal evaporation, or the like. And, an encapsulation layer made of a metal, a glass, or the like or a passivation layer made of an organic or an inorganic material is formed on an entire surface including the second electrodes 68 so as to make the organic light-emitting layers 67 vulnerable to moisture and oxygen airtight from the outside.
Moreover, a certain amount of the photoresist should remain at a bottom of the trenches 66 to prevent a short circuit between the first electrodes 62 and the metal of the second electrodes 68 deposited inside the trenches 66. Therefore, a thickness of the photoresist remaining inside the trenches 66 is controlled by controlling a flood exposure amount or a development time. In this case, the remaining thickness of the photoresist is preferably about 1 μm.
In the aforementioned third conventional organic electroluminescence display and the fabricating method thereof, a single process is carried out to form the insulating layer and the separators by using the half tone mask and the image-reversal photoresist, and the trenches are formed at the central portion of the separators, thereby simplifying the fabricating process. Further, since an adhesive strength problem between the insulating pattern and the separators and an alignment margin problem are not occurred, an opening ratio of the organic electroluminescence display can increase. However, it is difficult to design the half tone mask and, further, a product cost thereof increases in comparison with a conventional mask by about 1.5 times or more.
Such fabricating methods of the conventional organic electroluminescence display have following drawbacks.
In the first conventional organic electroluminescence display and the fabricating method thereof, the photolithographic process is carried out twice to form the insulating pattern and the separators. Therefore, the alignment margin needs to be guaranteed, which results in a decrease in the opening ratio. Further, the adhesive strength between the insulating layer and the separators becomes poor, and the fabricating process becomes complex, thereby increasing the product cost.
In the second and the third conventional organic electroluminescence display and the fabricating method thereof, a single process is carried out to form the insulating pattern and the separators by using the half tone mask. However, in this case, it is difficult to design the half tone mask, and a product cost thereof increases in comparison with a conventional mask by 1.5 times or more. Besides, in case of the second conventional organic electroluminescence display, since there is no overhang structure of the separators, a shadow mask having a stripe type pattern is required for a patterning of the second electrode. However, such shadow mask is not adaptable to currently mass-produced organic electroluminescence displays.